Tribalism is related to another problem in American politics: a blurring of the lines between opinion and fact, what the RAND Corporation in a recent study called "truth decay," whether it's liberals rejecting the safety of vaccines, conservatives rejecting evidence of Barack Obama's birth certificate, or conspiracy theories embraced at the highest levels of government.

Liasson is straining to keep this balanced: I've got one from the liberals, one from the conservatives, and one unspecified. Except, of course, the unspecified one refers to our Republican president, so it's two to one. And those liberal vaccine skeptics? I've been known to bash them, too, but liberals don't have a monopoly on vaccine trutherism.

Based on data released in 2014, here were the eleven states in which vaccine exemption rates for kindergartners exceeded 4%. Alex Berezow, writing Real Clear Science, appended each state's winning presidential candidate in 2012 and the candidate's margin of victory:

I see five blue states, four red states ... and two states, Wisconsin and Michigan, that were blue in 2012 and switched to Trump in 2016. So this is a bipartisan phenomenon. Also, one of the bluest states, California, passed a law in 2015 eliminating personal vaccine exemptions. Although parents who distrust vaccines are still finding a way around the law, vaccination rates reached an all-time high. That's how a liberal state dealt with its "truth decay" problem. Republicans dealt with theirs by choosing America's most famous birther as their presidential nominee and then electing him president.

If Democrats and Republicans can't agree on whether the planet is getting warmer or whether inner-city crime is going down, it's impossible to have a debate about solutions.

Do I have to explain what's wrong with this? According to Liasson, the problem is that the two parties can't agree -- not that Democrats believe the facts and Republicans believe fairy tales. The planet is warming -- that's objective fact. Democrats believe it. Republicans don't. Over the past couple of decades, inner-city crime has dropped dramatically, although there have been recent increases in some cities. Democrats acknowledge both the long-term pattern and the short-term reversals in some locales. Republicans cry "American carnage!" and claim that our cities are apocalyptic hellholes.

Liasson quotes William Galston of the Brookings Institution:

The percentage of Republicans who view Democrats as a threat to the Republic and vice versa has soared in recent years and now exceeds a majority in both tribes.

She says:

Many Republicans felt that way about Barack Obama. Many Democrats feel that way about Donald Trump.

But the Republicans who felt that way were wrong. After eight years of Obama, the Republic still stands. The damage they claimed to expect never materialized. It's impossible for any rational person to look back on the Obama presidency as an assault on America's laws and governing norms. The same can't be said about the Trump presidency.

Liasson ends with a note of hope:

Whether you're a woman or from an immigrant community running [for office] for the first time or a white working-class Trump supporter who voted for the first time two years ago, this renewed sense of civic responsibility is the first step to making the state of our politics less broken.

Yes, these people were clearly trying to make our politics "less broken":